Here's another ominous sign a nuclear deal with Iran won't work the way Obama wants it to

A worker rides a bicycle in front of the reactor building of a nuclear power plant, just outside the southern city of Bushehr, Iran. AP Images The New York Times recently reported that Iran's stockpile of 5% enriched uranium had grown by 20%, to over 8,700 kilograms, citing an International Atomic Energy Agency report.

A cap on Iran's 5% stockpiles at the end of the negotiating period was agreed to as part of the technical understanding s reached in early 2014 after the signing of the November 2013 Joint Plan of Action (JPOA).

At that point, Iran had 7,600 kg of 5% uranium. Today, it has 8,715 kg, meaning Tehran must slash its stockpile by over 1000 kg by the June 3oth deadline for a final nuclear agreement.

In reality, it's low-enriched uranium (LEU) stockpile is growing. Though true at the time, a July 22nd, 2014 US State Department claim that Iran had "capped its stockpile of 5 percent enriched uranium" shows that Iran's behavior, and possibly its assessment of the entire negotiating process, have changed over the past year.

Nevertheless, Obama administration officials quickly dissembled, with State Department communications advisor Marie Harf pushing back against New York Times reporter David Sanger on Twitter.

Supportive analysts argued that the increase wouldn't impact the coming nuclear agreement, with Max Fisher of Vox reaching the counter-intuitive conclusion that a growth in Iran's enriched uranium stockpile was unimportant because there was still "nothing preventing Iran" from reducing its stockpile once a deal is signed.

Reuters

But the increase casts doubt on another one of the pillars of a future Iran nuclear deal.

Based on the series of apparently unwritten understandings reached in Lausanne, Switzerland on April 2nd, Iran must get its stockpile of low-enriched uranium down to 300 kg under a final agreement.

Reuters So in order to reduce their stockpile to 300 KG, Iran would have to convert its uranium to fuel assemblies for its nuclear reactor in Bushehr. But reconversion is the part of the nuclear fuel cycle in which Iran's capabilities are the most lacking.

There's a fuel manufacturing plant in Isfahan, but it was at a rudimentary operational state in 2013, shortly before the JPOA halted certain aspects of the country's nuclear development.

Iran currently purchases fuel rods for Bushehr from Russia, partly because it doesn't have an industrial-scale capability to reconvert enriched uranium for peaceful use.

Sanger hinted in his New York Times article that the uranium stock has been growing for exactly this reason: There's been "a bottleneck at the new plant" for converting enriched uranium to fuel assemblies, although it's unknown if "technical problems, Iranian foot-dragging, or some combination of the two" are to blame.

In other words, Iran may not have the technical capabilities needed to keep their stock even within currently agreed limits — something that gives Tehran a built-in excuse for any gaps in compliance while raising the possibility that it won't be able to cull its LEU stock once a deal is actually signed.

And a deal can't work unless Iran scales back or exports its 5% stocks.

It's easy to imagine a future scenario in which Iran uses technical shortcomings as cover for keeping a larger LEU stock for a longer span of time than a final deal allows — something that could be a critical test of the US's willingness to punish Iranian intransigence in a post-deal environment.

Iran's Supreme Leader Ayatollah Ali Khamenei waves to a crowd in the holy city of Qom, 75 miles south of Tehran in 2010. Reuters

There's another, even more worrying explanation for the growth of Iran's 5% stock: The stockpile could be an insurance policy for the possible failure of the nuclear talks, as well as leverage for ensuring the talks actually conclude with a deal.

Iran how has nearly 9,000 kg of uranium that's gone through half the centrifuge revolutions needed for weapons grade, in addition to a supply of 20% uranium oxidized under the JPOA that could still be converted for weapons use in a matter of months.

If the talks collapse, Tehran can keep its options open — a possibility that US negotiators are surely aware of, regardless of what administration spokespeople are saying in public.